Sandwich gasification process for high-efficiency conversion of carbonaceous fuels to clean syngas with zero residual carbon discharge
The present invention discloses a gasifier and/or a gasification process that provides a long, uniform temperature zone in the gasifier, regardless of the particle size, chemical composition, and moisture content of the fuel by sandwiching a reduction zones between two oxidation zones. The gasifier and/or gasification process has a char that is more energy-dense and almost devoid of moisture that affords for an additional (or char) oxidation zone with a temperature that is higher than a first oxidation zone which is closer to a evaporation and devolatilization zone. As such, the additional (or char) oxidation zone contributes to augmenting the reduction zone temperature, thereby providing a favorable dual impact in improving syngas composition and near-complete conversion of the tar.
1. A mixed-mode gasification process comprising:
providing a gasifier having a fuel injection port and an ash or residue extraction port, a first exothermic oxidation zone, a second exothermic oxidation zone and an endothermic reduction zone located directly next to and sandwiched between the first and second exothermic oxidation zones, the first exothermic oxidation zone located on a side of the gasifier next to the fuel injection port and upstream from the endothermic reduction zone, the second exothermic oxidation zone located on a side of the gasifier next to the ash or residue extraction port and having a temperature higher than the first exothermic oxidation zone, the gasifier also having at least two different gasification medium injection zones and a syngas outlet located at the endothermic reduction zone;
providing at least two separate gasification medium;
providing one or multiple fuel streams to the same gasifier, wherein all fuel streams provided to the gasifier are provided to the gasifier upstream of the first oxidation zone;
devolatilizing the one or multiple fuel streams to form a char;
providing a portion of the char to the second exothermic oxidation zone;
providing one of the at least two separate gasification medium to the second exothermic oxidation zone to oxidize the char; and
controlling a volume and temperature of the at least two separate gasification medium independently.
2. The process of claim 1 , wherein the second exothermic oxidation zone is a char oxidation zone fueled by the oxidation of char, the char oxidation increasing the temperature of the second exothermic oxidation zone for achieving near-equilibrium gas composition.
3. The process of claim 2 , wherein there is complete carbon conversion of fuel during the mixed-mode gasification process.
4. The process of claim 2 , wherein the char oxidation zone is downstream of the endothermic reduction zone.
5. The process of claim 1 , wherein the second exothermic oxidation zone is fueled by char and heat from the second exothermic oxidation zone is used to augment the temperature of the endothermic reduction zone.
6. The process of claim 1 , wherein at least one of the gasification medium is selected from a group consisting of air, oxygen-enriched air and steam, and pure oxygen plus steam.
7. The process of claim 2 , wherein molten or solid ash is recovered downstream of the char oxidation zone.
8. The process of claim 1 , further including an evaporation and devolatilization zone located upstream of the first exothermic oxidation zone.
9. The process of claim 8 , wherein the evaporation and devolatilization zone is adjacent to the first exothermic oxidation zone.
10. The process of claim 1 , wherein the one or multiple fuel streams comprise fines and friable char.
11. The process of claim 1 , wherein the gasifier further comprises an annular space or chamber around the gasifier for receiving fuel.
12. The process of claim 11 , wherein large-sized fuels are fed to the annular space or chamber around the gasifier.
13. The process of claim 12 , wherein the large-sized fuels are devolatilized in the annular space or chamber around the gasifier to form devolatilized products and char.
14. The process of claim 13 , wherein the devolatilized products are injected into the gasifier for further conversion with the help of an oxidizer or carrier gas.
15. The process of claim 14 , wherein the large-sized fuel comprises automobile whole tires.
16. The process of claim 1 , wherein multiple fuel streams are provided to the same gasifier, wherein said multiple fuel streams comprise a primary fuel and a secondary fuel, and wherein said secondary fuel is formed within the gasification process.
17. The process of claim 1 , wherein multiple fuel streams are provided to the same gasifier, wherein said multiple fuel streams comprise a primary fuel and a secondary fuel, wherein said secondary fuel is formed within the gasification process, and wherein the primary and secondary fuel are fed to the gasifier from the same fuel injection port.
18. The process of claim 1 , wherein multiple fuel streams are provided to the same gasifier and wherein the multiple fuel streams comprise fines.
19. The process of claim 1 , further comprising operating the gasifier in a self-sustained gasification mode and wherein the fuel contains more than 50% inert matter.